1. Field of the Invention
The invention proceeds from a hydraulic actuator for actuating a valve. The actuator has a drive volume that is pressurized by extreme-pressure oil and is bounded by a drive piston. A spring element acts upon the drive piston in a manner opposing the extreme-pressure oil.
2. Discussion of Background
Hydraulic actuators for actuating valves in power stations are known such as are actuated by extreme-pressure oil and which are moved back once again into the initial position by an in-built spring element when the pressure of the extreme-pressure oil decreases or when the extreme-pressure oil is pumped off. As a rule, in this regard the drive volume and the spring element are arranged behind one another in the actuator on a common axis. This model requires a relatively large amount of space in the axial direction. In addition, the drive volume adjoins the ambient air at least on one side, so that in the event of seal damage extreme-pressure oil can escape from the drive volume and endanger the environment. Thus, for example, fires can be started by extreme-pressure oil spraying onto hot parts.